1. Technical Field
The present disclosure relates to high intensity focused ultrasound (HIFU) applications. More particularly, the present disclosure relates to systems and methods for tracking and guiding HIFU beams. Although exemplary embodiments relate primarily to acoustic hemostasis, the disclosed systems and methods apply to and for any HIFU application, including but not limited to HIFU treatments for uterine fibrosis, cancer, and cardiac arrhythmias, such as atrial fibrillation.
2. Background Art
Blood loss from extremity wounds is the number one cause of preventable battlefield death today. In civilian casualties, exsanguinations due to internal bleeding are the most significant cause of death in trauma victims. Hemostatic therapies such as HIFU and electrocautery may be used to quickly stop internal bleeding to prevent onset of progressive and irreversible hemorrhagic shock, which ultimately leads to death. The onset of bleeding must be detected and the site spatially localized in order to treat these trauma wounds effectively. As part of the DARPA DBAC program at Philips Research Briarcliff, 3D Doppler ultrasound based techniques have been developed to detect and localize a bleeding site (herein referred to as “Bleed Detection and Localization” or “BD&L”) automatically by tracking the change in quantitative parameters extracted from the Doppler spectra such as Resistance Index (RI). For these emergent care type applications, the device is designed to be operator independent and, therefore, image-based feedback allowing user interaction and control is not available.
Hence, an extremely essential component for success of HIFU based hemostasis treatments is the ability to continually track if the therapy is being delivered at the correct location. Due to tissue heterogeneities and lack of quantitative information on the local thermal and acoustic properties, there exist errors between the intended spatial location of treatment and the actual physical location of the HIFU focus. A tracking and guiding system must, therefore, actively refocus the HIFU beam to the desired location so that the therapy is delivered at the appropriate site without unwanted damage to surrounding normal tissue. Although BD&L techniques may be repeated to determine if a bleed rate has slowed or stopped, these techniques do not provide any quantitative feedback or spatial information relating to the optimal reorientation or refocusing of the therapy relative to the desired treatment location.
A number of researchers have proposed the use of B-mode images to provide imaging feedback and spatially locate the HIFU beam by tracking the presence of hyper-echogenicity. However, it has been demonstrated that this information is not always reliable since hyperecho can appear quite some time after the tissue has already been ablated and when the local tissue temperature is close to boiling. The inhomogeneous structure of tissue would make direct B-mode visualization of the focal region of HIFU preceding boiling even more challenging. See B. A. Rabkin, V. Zderic, and S. Vaezy, “Hyperecho in ultrasound images of HIFU therapy: involvement of cavitation,” Ultrasound Med Biol, vol. 31, pp. 947-56, 2005. An effective tracking method must be able to locate the HIFU focus without causing any damage to normal tissue.
The following U.S., foreign and PCT patents and publications provide examples of prior art relating to hemostasis and/or HIFU systems. In all cases, the disclosed systems and methods fail to provide adequate means for tracking and guiding therapeutic HIFU beams.
European Patent Publication No. EP0989822 describes a method of producing remote hemostasis within a patient body. The method involves identifying an internal bleeding site and focusing therapeutic ultrasound energy through tissue from a radiation source to coagulate blood adjacent to the site. An imaging transducer provides an image of a portion of a patient body having an internal bleeding site, typically using pulsed Doppler color flow imaging, elasticity imaging, an angiogram or the like. Thus, this patent publication describes a method for effecting hemostasis and the use of ultrasound methods to identify a bleed. In particular, the noted European publication does not describe a method for identifying the location of HIFU focus to ensure treatment of a desired location.
U.S. Patent Publication No. US2005/215899 describes a method for identifying ablated tissue using acoustic radiation force impulse imaging. The disclosed method involves generating acoustic radiation force impulse (ARFI) image data wherein a region of increased stiffness represents ablated tissue. ARFI is thus employed to determine the extent and size of an ablated region. The disclosure does not, however, propose a method of detecting the HIFU focus prior to commencing ablation in order to determine if the ablation will be applied at the desired site. In addition, the sonication for ARFI is not generated using the HIFU transducer.
PCT Publication No. WO2004075987 describes an HIFU delivery method for tracking and accounting for body movement of a subject patient. The disclosed method involves acquiring ultrasound image data of the patient's target area and comparing current image data with previously acquired image data. Discrepancies are analyzed in order to detect and account for patient movement prior to HIFU treatment administration. This patent publication does not involve the use of ARFI. Rather, the disclosure relies on using a sequence of ultrasound images to determine and account for movement. In addition, the disclosed technique does not detect the HIFU beam focus.
U.S. Patent Publication No. US2005/203399 describes an image guided HIFU device for therapy in obstetrics and gynecology. A frame ensures that the alignment between a high intensity focused ultrasound (HIFU) transducer designed for vaginal use and a commercially available ultrasound image probe is maintained, so that the HIFU focus remains in the image plane during HIFU therapy. This patent publication does not propose the use of ARFI to determine the location of the HIFU focus. The proposed mechanical frame is specifically applicable for the transducer geometry in obstetrics and gynecology and cannot be extended for other clinical applications of HIFU. Furthermore, the HIFU focus position is determined only within a 2D plane.
Despite efforts to date, a need remains for systems and methods for effective tracking and guiding HIFU beams. These and other needs are satisfied by the present disclosure, as will be apparent from the description which follows.